1. Field of the Invention
The present invention relates to method and apparatus for inferring position of an oxygen lance within the molten metal environment of an electric arc furnace or the like. Position is inferred by comparing sound characteristics actually encountered with predetermined sound characteristics typical of the various operating stages and conditions of the metal making process.
2. Description of the Prior Art
In furnaces for making steel from a metal charge such as steel scrap, a lance for injecting an oxidant gas, such as oxygen, is employed to speed up the melting process, to reduce refining time, to create a foamy slag, and to influence characteristics of the final steel composition. Oxidant injection is preferably conducted at precise locations with respect to the level of molten metal and slag within a furnace. It is necessary to adjust the position of the lance from time to time during this process, as to compensate for greater or lesser quantities of metal and slag in the furnace due to material addition and withdrawal, or to control the rate of injection of oxidant as may be appropriate.
Direct observation of the level of a molten metal stratum existing within the furnace is nearly impossible. Severe heat, violent currents of vapors above the liquid phase, and roiling of the liquids present all obstruct observation. Traditionally, the industry has relied in part upon the experience of a human operator to adjust position. The operator may be assisted by a technique such as analysis of gas escaping from the furnace, which may lead to inferences relating to relevant conditions existing within the furnace.
The prior art has attempted to further the effectiveness of methods of observing internal furnace conditions, and the following two examples are based upon monitoring sonic characteristics. U.S. Pat. No. 4,530,102, issued to Steven S. Baker et al. on Jul. 16, 1985, discloses a method of controlling lance position by recording and analyzing sonic emissions from a steel furnace. A directional microphone is located outside the furnace, and is aimed theretowards. Sonic emissions are monitored and compared to sonic characteristics which are predetermined to correlate to various possible furnace conditions. The lance is then adjusted as appropriate in light of the comparison.
U.S. Pat. No. 3,701,518, issued to Louis M. Herff on Oct. 31, 1972, provides a method of controlling lance immersion by radar. An electromagnetic wave is generated and transmitted into the melt from the lance. This wave is reflected from a furnace surface back to a receiver, which may also be located within the lance. The characteristics of the received waves are then employed to derive inferences regarding existing conditions within the furnace, and the lance is adjusted accordingly.